Embrittled silver solder bonded abrasive



April 8, 1947. l A STERN 2,418,529

EMBRITTLED SILVER SOLDER BONDED ABRASIVE Filed Dec. 4, 1944 PatentedApr. 8, 1947 ERIBRITTLED SILVER SOLDER BONDED ABRASIVE Albert Stern,Chicago, Ill.

Application December 4, 1944, Serial No. 566,555

`i Claims.

AMy invention relates to a grinding wheel and more particularly to oneutilizing diamond for its cutting action.

In grinding wheels the cutting action of the abrasive particles is atpeak eiciency only when each particle may present unencumbered cuttingedges to the material being worked upon. One of the principal drawbacksin the use of abrasive Wheels is termed glazing, caused by par.. ticlesof material removed from the work embedding themselves in the spacesintermediate the cutting particles and thus interfering with the freeaction of the cutting edges. When glazing occurs it will rapidly buildup to a stage where the wheel must be redressed to expose a freshsurface of abrasive to the Work. Not only is this wasteful because ofthe discarded abrasive removed by the dressing operation but the workmust be discontinued until dressing has been accomplished. Thus, usefulproduction time is sacriiced. FurthermoreLin thecase of diamond wheels`dressing is a slow and difficult operation.

Many attempts have been made to overcome glazing and eliminateredressing but without success, as the material thus far used to bondthe wheel is generally of the same degree of plasticity and hardness asthe particles of metal removed from'the Work and the bonding agent andthe particles therefore conglomerate into a homogeneous mass Where theoriginal intention was that the particles of metal should embedthemselves in the bonding agent and leave uninterrupted abrasive cuttingparticles projecting from the surface of the wheel.

I have found that anon-glazing Wheel may be constructed in which thematrix comprises the principal abrasive ingredient, for example,diamond, together with another abrasive ingredient, for example, siliconcarbide, and a bonding and filling agent including ilakelets of mica andsilver solder. While the theory of operation of my wheel is not thus farfully understood, one theory of operation seems to be that the mica andsilver solder together form a sufficiently dense and tenacious bondingagent while being subject to easy attrition as the wheel wears in use.This may be due in part to the aky nature of mica which imparts alubricating quality permitting superimposed akelets to slide one uponthe other and be severed from the mass. Thus, as grinding proceeds, theparticles 'of metal removed by the wheel will dislodge the nakelets andthe silver solder dispersed between the abrasive parseries ofcuttingfedges of the abrasive proper to be presented to the work.

Accordingly, the principal object of my invention is to provide anon-glazing grinding wheel in which the abrasive particles including oneor more cutting materials are embedded in a matrix including comminutedmica and silver solder.

An additional object of my invention is t0 provide a non-glazinggrinding Wheel in which the matrix is of such character as to providecleavage planes in the bonding agent.

Still another object is to provide a non-glazing grinding wheelincluding material subject to easy cleavage combined with materialserving as a bonding agent for the abrasive particles.

Other objects are to provide a grinding wheel which will enable drygrinding to be done without glazing and to decrease the time of agrinding operation.

A further object of the invention is to provide a grinding wheel whichis cooler in o ration.

Another object is to enable the production of wheels of various gradesby variation in the proportion of mica content.

An additional object is to provide a wheel including mica as part of thematrix whereby the latter is less brittle and hence not easily subjectto breakage in use.

Other objects will appear as the description proceeds.

In the drawings:

Fig. 1 is substantially a diagrammatic view of an apparatus in which thegrinding wheel of the invention may be fabricated;

Fig. 2 is a diametrical cross section of a grinding wheel of the cuptype embodying a grinding portion in accordance with my invention;

Fig. 3 is a magnified 'view through a portion of the work and a portionof the wheel, the cross section being taken to show the relativemovement between the abrasive surface and the work; and

Fig. 4 is a fragmental portion of Fig 3 on an even greater enlargedscale intended to show the theory of operation of my new wheel.

Referring rst to Fig. 1, there is a hollow cylindrical molding chamber 9in the aperture I0 of which is deposited a series of wheel blanks IIcylindrical in form and including a plurality of concentric keyinggrooves I2 adjacent the outer periphery of one fiat face I3 thereof..Adjacent the face I3 of each blank II is a molding element I4 having aperipheral recess I5 .of cross section to correspond with the contour ofthe ticles and continuously allow a freshly exposed grinding surface tobe produced, i. e., rectangular, 'semi-circular, etc. Each of the blanksand' units Il is pierced with a substantially central aperture IB, allin alignment.

In loading the chamber 8 there is first placed on the bottom a mass of asuitable fusible or t thermoplastic bonding agent 20, e. g., silversolder, then a molding element I4 with its recess I5 uppermost. In therecess is substantially uniformly distributed material comprising amixed predetern ined quantity 2| of principal abrasive particles. e. g.,diamond of a mesh suitable for the work to be performed by the wheel andof substantially uniform mesh, comminuted abrasive material of ahardness less than diamond, for example, silicon carbide, availablecommercially in one form under the trade name Carborundum, andpreferably of iiner mesh than the principal particles, andA comminutedmica which, due to the nature of the material, will be yielded asminuteflakelets. A sufficient quantity 0f this mixture is distributedloosely into and piled slightly over the recess I5, the quantitybeing'measured in advance and determined upon empirically. After themixture 2| is thus deposited a wheel blank is set into place as shown.Then another complete unit comprising an element I4, a mass of themixture 2|, 'and a wheel blank is set in position, and so on, therebeing as many sets as is permitted by the capacity of the moldingmachine.

The entire molding unit is encased in a shield 22 extending upwardlyinto a hood 23 having a vent opening 24. Through apertures in the sidesof the enclosure 22 extend a plurality of heating jets 25, only twobeing shown for clarity. Illuminating gas or any other suitablecombustible fluid may be admitted to the jets 25 and ignited so that theflames play upon the outer-,surface of the chamber 9. The contents ofthe chamber, including the bonding agent 20 will be raised intemperature and when the agent reaches flowing temperature a piston 26at the lower end of a screw 21 and fitting the aperture i0 is broughtdown upon the contents of the chamber, the pressure being sufiicient todisplace the melted mass of agent 20upwardly through the centralopenings I6 -and then radially outwardly in the spaces 28 :intermediateeach blank and element I4 and into the interstices of the mixture 2|.

The pressure is applied gradually and the agent v sustained in meltedcondition until the gaps 28 are entirely closed. When this occurs themass of abrasive material, bonding agent and mica has been pressed intoa homogeneous solid mass of the desired dimensions. Part of this massenters the grooves |2 which serve to lock'the annular abrasive portionproper of the wheel rmly to the wheel blank Il. Piston 26 is retracted,the chamber 9 allowed to cool, and the several complete wheel units maythen be withdrawn.

The wheel units may be used in disc-like form as shown in Fig. 1 or maybe turned on a lathe to any other desired shape, for example, cupped,

`as shown in Fig. 2.

ticles 3|, e. g., diamond, sometimes commercially y 4' in comminutedform and ofa mesh finer than the bort, and 331/3% of mica akelets of amesh finer than the bort. The silver solder or otherv bonding agentwhichk bonds the entire matrix is not to be considered a part of theproportions of the mix but only as a bonding agent. It will beunderstood that the size of the recess I5 and `0|! the gap 28 may be sodesigned with respect to the amount of abrasive and the mica that onlysuilicient bonding agent to effect a thorough bond will be permitted toflow for formation of .a niatrix of the desired proportions.

In operation the particles of diamond will perform the major part of thegrinding operation and these will be assisted by the particles ofsilicon carbide. However, it is intended that the latter named particlesshall have a glaze-preventing action. 'I'hat is, as attrition of thewheel occurs the particles of silicon carbide will be permitted to movewithin the mass to permit breaking down of the bonding agent and toassist in the movement of the mica flakelets. Otherwise stated, theaction is intended to be similar to that occurring in a ball mill.

The mica iiakelets, at least according to my theory of operation, tendto separate the bonding agent into disconnected strata. Hence, asattrition occurs those particles of silver solder near the surface slidefreely on the mica flakelets and on each other and are carried away,either by the air stream in dry grinding or the lubricant in wetgrinding, thereby leaving a constantly exposed cutting surf ace ofdiamond.

In Fig. 4, the reference numeral 35 indicates a high spot of the workwhich the grinding operation is intended to remove and it is shownmidway between two diamond particles 3| and 3Ia. It is intended that aparticular diamond particle 3 la shall be the next t0 perform thecutting operation and it will be noted that the highv not limited to adiamond wheel but is capable of being embodied in any type of wheel, forexample, one including silicon carbide alone as the abrasive agent. Thegist of the invention resides in the inclusion of the mica fiakeletswith thematrlx, and by mica I refer to any of those minerals commonlysold under the name mica,

there being several ,technically'diiferent types found in nature.However, they are all charac terized by forming flakelets whencomminuted, the natural planes of cleavage of -mica yielding thinplaniform particles or wafers having distinctive lubricating qualitieswhen in such form.

One important advantage in the use of mica for the purpose outlined isits extreme resistance to disintegration under heat. Thus, although thewheel may reach a high temperature in operation, the mica fiakelets willnot break down into a form not possessing the desired characteristicsoutlined hereinabove. Notwithstanding the fact that the wheel may reachrelatively high .temperatures in operation during dry grinding, itissubstantially cooler when wet grinding is being done. By reason of thefact that the mica is friable, pores are created in the matrix asgrind-- ing proceeds. These pores impart a spongy characteristic to thewheel enabling it to absorb substantial quantities of water and to coolthe wheel.

Since the mica is a material relatively softer than the otheringredients of the wheel, it is possible, by varying the proportion ofmica, to construct wheels of varying degrees of hardness. Such gradationin the so-called hardness" of the wheel renders the same exactly suitedto the type of work being done. Metal bonded diamond wheels now known tothe art are incapable of being so controlled in hardness.

Inasmuch as the wheel of my invention is, generally speaking, softerthan other diamond wheels, it is not as subject to breakage, the matrixbeing more brous in nature as contrasted with the brittle constructionof wheels presently known.

Trial has shown that the Yimproved wheel of my invention is capable ofincreasing production as much as 30% over similar wheels notincorporating my improved matrix and that this increase is-due to thenon-glazing characteristic thus achieved.

Although I have shown by way'of illustration the invention embodied in agrinding wheel, it will be comprehended that the abrasive composition iscapable of use in other forms, for example, awhetstone.

Further modifications will be apparent to those skilled in the art andit is desired, therefore, that the invention be limited only by thescope of the appended claims. Y

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. A substantially non-glazing abrasive body comprising a bonding matrixof silver solder having embedded therein substantial quantities of s ingembedded therein substantial quantities each of diamond particles ofsubstantially uniform size and silicon carbide and mica particles thatare both smaller in size than said diamond particles.

10 3. A substantially non-glazing abrasive body comprising a silversolder bonding matrix having embedded therein substantial quantitieseach of abrasive particles of substantially uniform size and micaparticles that are smaller in size than 15 said abrasive particles.

4. A substantially non-glazing abrasive body comprising a bonding matrixoi' silver solder having embedded therein about equal parts each ofsilicon carbide particles of substantially uniform 2o size and micaparticles that are smaller in size than said silicon carbide particles.

ALBERT STERN.

25 REFERENCES CITED 1 UNITED sTA'rEs PATENTS 30 Number Name l Date1,907,088 Novotny May 2, 1933 2,197,655 Boyer f l Apr. 16, 19402,223,063 Fitz-Randolph Nov. 26, 1940 2,306,423

Bemtorl! et al. Dec. 29, 190

